By means of supplementing the sight part for incoming visible light, the so-called day sight, with an IR camera, a sight is obtained which can also be used in the dark and in bad weather, a so-called night sight. The invisible thermal radiation from the terrain is converted into an image which is visible to the eye. The image is reflected into the day sight using a beam splitter.
Under normal daylight conditions, the daysight image is many times brighter than the image coming from the night sight and therefore completely dominates the image of the terrain which an observer sees. Under certain circumstances, however, it is of interest to be able to use the IR sight during daytime as well. In order to achieve this, it is known to introduce a filter, which in principle excludes all daylight, into the beam path for incoming visible light. When such a filter is present in the beam path, information about the terrain is obtained solely in the IR range.